1. Field of the Invention
The present invention relates to an Orthogonal Frequency Division Multiplexing (OFDM) receiver, OFDM receiving circuit and an OFDM reception method using diversity, and more particularly relates to an OFDM receiver, OFDM receiving circuit and an OFDM diversity reception method which lowers the error rate and enhances the reception quality level.
2. Description of the Prior Art
OFDM is a modulation technique that enables transmission of a large number of individual carrier waves, commonly called carriers, at a high spectral density level which are orthogonally spaced in frequency and therefore do not interfere with each other within a transmission bandwidth. The data streams are allocated in the amplitude and phase of each carrier and digital modulation is implemented, such as Phase Shift Keying (PSK), Quadrature Amplitude Modulation (QAM), etc. For example, the digital terrestrial broadcasting standard (ISDB-T: Integrated Services Digital Broadcasting-Terrestrial) in Japan allocates 6 MHz of frequency spectrum per channel and each 6 MHz bandwidth is divided into 13 parts called segments. In this manner, by orthogonally multiplexing a plurality of carriers in each segment, High Definition Television (HDTV) broadcasting, Standard Television (SDTV) broadcasting and simplified broadcasting for mobile applications can be accomplished.
Furthermore, the OFDM receiver uses a diversity system for improving reception capability. This technique receives radio waves transmitted by a broadcasting station with multiple antennas. Maximum value composite signal processing is performed with these multiple antennas and the highest signal reception quality (referred to as C/N or Carrier to Noise Ratio which is the measured ratio in dB) is always chosen and outputted. Subsequently, the highest signal reception quality is transformed into a digital signal and demodulation processing is performed in a demodulator circuit. Thus, the effect of fading on transmission lines, etc. is kept to a minimum.
However, in the conventional diversity system mentioned above, there is a drawback with sufficient reception quality for accurately and reliably demodulating the received data in a multipath situation which often occurs between large urban buildings, etc. particularly since diversity is performed based on the time domain signal.